The present invention relates to a binary facsimile image signal coding method, and more particularly to a facsimile image signal coding method which is effective for efficient data compression of a printed document or the like.
In recent years facsimile has startlingly spread by virtue of its advantage that it is able to easily transmit, as images, any forms of documents with no limitations imposed thereon. Facsimile possesses the abovesaid advantage, but on the other hand, since it encodes data as photographic elements, the encoding efficiency is not high in case of complex documents. In particular, in a case where character elements such as printed characters are encoded using a conventional facsimile encoding system, the encoding efficiency is lower than 1/10 that in case of encoding character elements using character codes. In recent facsimile communications, documents containing printed characters are transmitted, and studies are now being made of an encoding system which permits high efficiency processing of such character data.
In general, the prior art described above achieves a high coding efficiency in a case where the same character pattern appears many times and a few number of library patterns are registered in a pattern library, as in the case of a printed document. For a handwritten document, a graphic document and so forth, however, since the number of appearances of the same pattern in these documents is extremely small, the coding efficiency of the above-mentioned prior art is lower than that of a two-dimensional coding system (Modified Read system) recognized as an international standard coding system by CCITT. According to this coding system, even a matching pattern which appears only once in the input image must be registered in pattern libraries on both the transmitting and the receiving side, and in particular, the graphic pattern must be sent from the transmitting side to the receiving side, together with the positional coordinates, the size and the identification code, so that the coding efficiency is lower than that obtainable with the two-dimensional coding system which sends only the graphic pattern in principle.